man i swear i had a post on this but i guess i never hit publish
In the gist:
go to a free script site like hotscripts and grab a simple whois lookup script
grab a list of nic servers and throw them in.
In the portion of the script that prints out the contact info grab the variable that holds the email address and write that out to a flat file or your db (whatever you're using).
Remove the variable that pulls the domain to lookup from the form and replace it with an array of all the domains you want to pull.
Then put the whole script in a while loop to go through the array.
it's easier than it sounds and better than starting from scratch.